As a conventional art related to a gland packing which is used in a shaft seal part of a fluid apparatus such as a pump or a valve, or a yarn (braiding yarn) used in it, a configuration which uses expanded graphite is conventionally known. Patent Literature 1 and Patent Literature 2 disclose configurations which use PTEE (polytetrafluoroethylene) in addition to expanded graphite.
Namely, the configurations were created with the objective of, while maintaining a high compression restoration property and adaptability which are original properties of expanded graphite, forming a yarn in which the tensile strength and the toughness are high, and which therefore can exert a high sealing property as a packing. However, the configurations of Patent Literature 1 and 2 have the following problem.
The configurations are formed by winding a sheet of PTEE or the like around expanded graphite or high-strength material which functions as a core, or by laminating PTEE to the surface of an expanded graphite tape. Therefore, the core material (expanded graphite) is easily exposed. Since the sheet is spirally wound, there is also a disadvantage that their production requires a relatively long time.
In summary, in a yarn produced by the winding (spiral winding) method, since a sheet made of PTEE or the like is wound around a core member, the core material tends to be exposed, and a long production time is required. In a yarn produced by the laminate method, a problem that the core member is exposed from both end portions of the sheet remains to be solved.